NAVAL FACILITIES ENGINEERING COMMAND Washington, DC 20374-5065
NFESC
Technical Report
TR-2219-ENV
Surfactant-Enhanced Aquifer Remediation
(SEAR) Implementation Manual
Prepared by:
Intera Inc. (formerly Duke Engineering & Services)
and
Naval Facilities Engineering Service Center
April 2003
ACKNOWLEDGEMENTS
The initial version of this document was prepared by John Londergan at Intera, Inc. (formerly Duke Engineering & Services of Austin, TX). The final content editing and revision of this document has been performed by Laura Yeh of the Naval Facilities Engineering Service Center, who acknowledges her co-author, the influences of many peers and colleagues, including those in related fields, as well as feedback related to parallel documents and projects in progress, under the lead sponsorship of other organizations and agencies. The contributors to the first SEAR Design Manual are greatly thanked for their assistance.
CONTENTS
ACKNOWLEDGEMENTS ...i
CONTENTS...ii
FIGURES ...iii
TABLES...iii
ACRONYMS AND ABBREVIATIONS ...iv
Section 1.0: INTRODUCTION
...1
1.1 Objective and Scope... 1
1.2 Technology Review... 1
1.3 Document Organization ... 2
Section 2.0: FIELD PLANNING ACTIVITIES
...4
2.1 Teaming... 4
2.2 Health & Safety... 4
2.3 Regulatory/Permitting Issues ... 4
2.4 Risk Management Issues ... 6
2.5 Performance Assessment... 7
2.6 Site Coordination Requirements ... 9
2.6.1 Water and Utilities... 9
2.6.2 Miscellaneous Logistics Issues... 9
2.7 Pilot-Scale Investigations ... 10
Section 3.0: SEAR SYSTEM COMPONENTS
...12
3.1 Component Description... 12
3.1.1 Chemicals Preparation ... 12
3.1.1.1 Batch Preparation Method... 12
3.1.1.2 In-line Mixing Method ... 14
3.1.1.3 Pre-mixing or Offsite Chemical Preparation ... 14
3.1.2 Injection and Extraction Operations ... 14
3.1.2.1 Injection and Extraction Wells ... 14
3.1.2.2 Pumps and Plumbing ... 16
3.1.3 Monitoring System Parameters... 17
3.1.4 Process Control System ... 19
3.1.5 Wastewater Treatment ... 19
3.2 System Components Preparation... 21
Section 4.0: FIELD OPERATIONS
...22
4.1 System Initiation... 22
4.2 Flooding Operations... 22
4.2.1 Injection Preparation and Quality... 23
4.2.1.2 Surfactant Injectate Preparation ... 23
4.2.1.3 Injectate Quality Control Measures... 23
4.2.2 Monitoring Evaluation of Flooding Operations... 24
4.2.2.1 Flowrate, Water Level, and DNAPL Level Monitoring... 24
4.2.2.2 Effluent and Monitoring Sampling... 25
4.2.2.3 Wastewater Treatment Monitoring... 28
4.2.3 Sample Analysis... 29
4.2.3.1. Surfactant Analysis ... 29
4.2.3.2 Analysis of Organics in the Presence of Surfactants... 30
4.2.3.3 Other Sample Analysis ... 30
4.2.4 Equipment Maintenance ... 30
APPENDICES ...33
APPENDIX A. SURFACTANT FLOODING WELL CONSTRUCTION SPECIFICATIONS ... A-1 APPENDIX B. MULTI-LEVEL SAMPLERS ... B-1 APPENDIX C. SURFACTANT TITRATION PROCEDURES FOR SODIUM DIHEXYLSULFOSUCCINATE... C-1 APPENDIX D. COMPARISON OF FIELD DATA TO PREDICTED SEAR SIMULATION RESULTS... D-1 APPENDIX E. CONTRACTING GUIDANCE FOR REMEDIAL PROJECT MANAGERS ... E-1
FIGURES
Figure 1-1. Flow Chart for Surfactant Flooding Implementation... 3Figure 3-1. HDPE Storage Tanks Used for Blending Electrolyte Solutions ... 13
Figure 3-2. Basic Surfactant Flooding Components Diagram... 15
Figure 3-3. Temporary Tented Wastewater Treatment Facility ... 20
Figure 4-1. Potentiometric Surface Map of Water Levels During Surfactant Flooding Operations... 26
Figure 4-2. Visual Monitoring Samples Collected from a SEAR Pilot Test... 27
TABLES
Table 3-1. SEAR System Monitoring Parameters ... 18ACRONYMS AND ABBREVIATIONS
CERCLA Comprehensive Environmental Response, Compensation and Liability Act cP centipoise
DAS data acquisition system
DNAPL dense nonaqueous phase liquid DQO data quality objective
FID flame ionization detector
GC gas chromatograph(y)
GFI ground fault interruptors HDPE high density polyethylene
HPLC high performance liquid chromatography ICP inductively coupled plasma
IFT interfacial tension
LNAPL light nonaqueous phase liquid MCL maximum contaminant levels mL milliliter
MLS multi-level sampler
NaCl sodium chloride
NAPL nonaqueous phase liquid
NPDES National Pollutant Discharge Elimination System PCE tetrachloroethylene or perchloroethylene
PITT partitioning interwell tracer tests POTW public-owned treatment works PPE personal protective equipment
RCRA Resource Conservation and Recovery Act RFP request for proposal
SCADA Supervisory Control and Data Acquisition SDWA Safe Drinking Water Act
SEAR Surfactant-enhanced aquifer remediation
SOW Statement of Work
TCD thermal conductivity detector TCE trichloroethylene UIC Underground Injection Control
USDW underground sources of drinking water
UTCHEM University of Texas Chemical Flooding Simulator VOC volatile organic compound
Section 1.0: INTRODUCTION
1.1 Objective and Scope
The objective of this implementation manual is to familiarize remedial project managers and engineers and scientists affiliated with environmental remediation projects on the major tasks and planning parameters involved with implementing an in-situ surfactant flood or surfactant-enhanced aquifer remediation (SEAR) project to remove dense non-aqueous phase liquids (DNAPLs). A companion technical manual has been produced on SEAR design focusing on removal of DNAPLs. It is hoped that in combination, the guiding principles presented in these two manuals will assist users in understanding basic design and implementation issues for attaining remedial objectives and in following risk management methodologies and approaches for avoiding misapplication of surfactant flooding for DNAPL removal. Cost-effective surfactant flooding performance demands recognition of the chemical flooding process, system specifications, and design and operational limitations, in order to secure the appropriate level of services and performance for the site.
This manual acknowledges that most key design parameters for surfactant flooding operations have been determined with earlier process design (as covered in the SEAR Design Manual) and that technology implementation on a full-scale is intended, or that a requirement for a pilot-scale study exists to fully specify design parameters. Planning and field preparation aspects, general system component specifications, and performance-related issues will be detailed. As can be discerned from the design criteria introduced within the SEAR Design Manual, surfactant flooding mandates expertise in many diverse areas inclusive of DNAPL source zone characterization technologies, aquifer and aquitard testing methods, and the chemical and multi-phase fluid flow properties of pumped surfactant solutions. Field implementation will furthermore require skilled knowledge of field-scale chemical preparation methods and remediation engineering resources for controlled injection and extraction of chemical solutions throughout the contaminated aquifer zones, and decontamination of the remedial fluids. 1.2 Technology Review
SEAR is a technology addressing the removal of immiscible-phase liquid contaminants, also termed nonaqueous phase liquids (NAPLs), from the saturated zone. In recent years, it has been further developed to be applicable to the removal of dense NAPL contaminants or DNAPLs such as TCE and PCE, which are amongst the most recalcitrant groundwater contaminants to be addressed in source zones or contamination source areas. Often likened as a chemical enhancement to pump and treat operations, aggressive source reduction technologies such as SEAR will typically be used in conjunction with conventional dissolved-phase remediation methodologies to restore groundwater quality to drinking water standards. The use of surfactants in a flooding configuration enhances the solubility and mobility of NAPL trapped in pore spaces to greatly increase the removal rate achievable with pumped groundwater. By promoting the rapid removal of these non-aqueous phase contaminants, groundwater cleanup goals may be accomplished more quickly.
Surfactant flooding involves the preparation of low viscosity surfactant solutions that are pumped through the DNAPL contaminated zone by introduction at injection points and removal from extraction points. Polymer amendment that will increase the viscosity of the surfactant solution may be required for higher viscosity contaminants (e.g., creosote) when temperature augmentation for viscosity reduction is not otherwise feasible. The surfactant flooding wellfield will generally be composed of dedicated surfactant injection and extraction points, and ‘water’ injection points for hydraulic control. Detailed site characterization is necessary to define DNAPL zone boundaries, and to elucidate the
minimize the risk of unintended DNAPL migration. Hydraulic continuity between the injection and extraction points is required to recover contaminated fluids and injectants, and such should be verified before injecting surfactants. When present, free-phase or mobile DNAPL1 will be evacuated through pumping and water flooding operations prior to surfactant solution injection to minimize the possibility of vertical DNAPL mobilization with interfacial tension reduction of the surfactant. The more tightly held DNAPL, also termed residual DNAPL, will then be removed through sweeping of the surfactant solution across the DNAPL source zone. A post surfactant-injection water flood is finally conducted to recover injected chemicals and solubilized or mobilized DNAPL remaining in the aquifer. Extracted fluids are treated above ground to remove free-product DNAPL, dissolved-phase contamination and cosolvent or alcohol injected with surfactants. Upon contaminant removal, the surfactant and cosolvent (usually residual from earlier treatment) can be recovered for reinjection, as desirable.
The greater the interfacial tension (IFT) requirements (i.e., low IFT value to be obtained with the surfactant system from a high IFT value without surfactants present) to accomplish surfactant-enhanced recovery of DNAPL, such as decreasing system permeability with greater capillary forces, the greater the necessity for appropriate hydraulic gradients to ensure recovery of DNAPL. Similarly, as contaminants are more readily mobilized in a permeable aquifer (e.g., requires less IFT reduction), high pumping rates and gradients that are also more easily accomplished in a permeable aquifer, will still be required to capture any mobilized DNAPL fluids. Field testing of interwell pumping rates for injection and extraction is required ahead of surfactant injection to verify sustainable pumping gradients.
1.3 Document Organization
The design manual includes issues related to technology applicability, design concepts and terminology, DNAPL source zone characterization, surfactant selection, wastewater treatment technologies, wellfield configuration and optimizing key flooding parameters for fluids delivery and recovery. This manual highlights project management planning issues, post-process design or field preparation and system construction requirements, system construction components, and major injection and extraction operational requirements. Following this overview section, surfactant flooding implementation topics are organized as follows: Section 2.0 describes field planning activities and issues, such as performance assessment, site logistics and the benefits of pilot-scale studies. Section 3.0 details the primary system components and assembly issues organized by major field task. Section 4.0 covers flooding operations, including preparation, monitoring and chemical analysis of SEAR fluids, and system shutdown. References, citations and miscellaneous details are footnoted throughout the document. Detailed specifications, methods and examples, including contracting guidance, may be viewed in the Appendices. The Figure 1-1 flowchart illustrates the basic decision steps for guiding field implementation of surfactant flooding projects.
1 United States Environmental Protection Agency. 1993. Appendix D – Glossary. Groundwater Sampling – A
Conduct SEAR design (Refer to SEAR Design Manual for additional discussion and for procedures)
1. DNAPL site characterization:
Includes document reviews,DNAPL delineation, lithology data, capillary barrier characterization and pumped aquifer testing
Conceptual groundwater model development
2. Develop or customize surfactant formulation:
Select type of surfactant flood and type of mobility control as needed Conduct surfactant testing with site groundwater and soils Add surfactant parameters for multi-phase fluid flow modeling
3. Finalize well spacing and pumping flowrates for hydraulic capture of dense contaminated surfactant fluids
Sensitivity analyses study of multi-phase fluid flow model
4. Select above-ground fluid processing using bench-scale testing as required
Too much uncertainty in the Lithologic and/or hydraulic site data? (e.g.,conflicting reported data or
data gaps)
yes investigation to optimizeProceed with pilot study
key operating parameters for mobility control measures yes
no
yes
Prepare or update planning documents and obtain required permits for
surfactant flooding project
Revise remedial objectives if desired, and determine
appropriate detail of Mobilize, Assemble
and Install SEAR System Conduct any additional
pre-remediation performance assessment characterization measures
Conduct surfactant flooding operations with performance monitoring sufficient to maintain hydraulic capture
of surfactant-laden DNAPL fluids
Evaluate performance data and conduct any post-remediation
site assessment measures as needed
no Re-evaluate remedial alternatives If additional DNAPL is
detected, delineate fully, and reconsider well screen intervals, well spacings and flowrates as relevant. Use appropriate tools to
confirm hydraulic continuity, and perform pumping testing for sustainable pumping rates
on all aquifer layers (i.e.,permeabilities)
to be flooded
CAUTION: If you skip this step, you may accidentally drop DNAPL
in the aquifer.
Was technology performance acceptable
and additional DNAPL to be removed?
Is site with highly variable hydraulic conductivities?
no
Conduct Corrective Action or pilot study as recommended or requested Evacuate free-phase DNAPL that accumulates within newly installed surfactant flooding and monitoring wellfield
Scale-up flood based on performance data
CAUTION: If you skip this step, you may accidentally drop DNAPL
Section 2.0: FIELD PLANNING ACTIVITIES 2.1 Teaming
Due to the multi-disciplinary nature of field activities, the technical team composition should include: geologists/hydrogeologists with groundwater remediation and modeling experience; environmental engineers with backgrounds in pumping systems, piping and instrumentation, wastewater treatment processes, power systems, and construction; chemical or petroleum engineers that are knowledgeable in surfactant chemistry, soil and groundwater physical and chemical properties, and the design of flooding remediation processes involving multi-phase fluid flow; and analytical chemists familiar with surfactant analytical techniques. For custom surfactant requirements, microbiologists, toxicologists, and process chemists should be included on the team to ensure food-grade or biodegradability requirements are being met, alongside consistent chemical delivery quality. The installed surfactant flooding system should have a high reliability in maintaining a constant quality of delivered surfactant solutions, continuous injection and extraction rates meeting required forced gradients for hydraulic capture, and treatment of extracted solutions to comply with discharge and reinjection requirements. Such will require a thorough understanding of the aquifer system in which the flooding system is emplaced, leading to proper location and installation of all wells for high efficiency pumping2,3 and DNAPL removal operations, as well as knowledge of positive and negative surfactant interactions within the contaminated aquifer environment and indicators of both responses for controlling and monitoring field operations appropriately.
2.2 Health & Safety
The primary hazard of SEAR operational activities is associated with the large quantities of DNAPL-contaminated fluids being extracted from the subsurface. Piping, hosing, and other plumbing lines that carry DNAPL-contaminated fluids should be chemically compatible with handled fluids so as to not leak during operations. Proper safety precautions will be required for handling these fluids during daily operations. Secondary containment is required of DNAPL storage tanks and all chemical waste and storage tanks. Air emissions monitoring may be required for volatile contaminants, e.g., chlorinated solvents and fuel components. A secondary chemical hazard is related to the transport, storage and handling of alcohol that will be used as cosolvent in the surfactant solution. Fire and explosion hazards exist due to the flammability of the alcohol. Alcohol drums should be properly grounded to avoid static electricity hazards. Compliance with OSHA and local regulations for work on hazardous waste sites will be appropriate for surfactant flooding projects.
2.3 Regulatory/Permitting Issues
Injection wells are regulated by the underground injection control (UIC) program under the federal Safe Drinking Water Act (SDWA). The purpose of the UIC program is to protect underground sources of drinking water (USDWs). Under the UIC program, injection of any fluid into a well is prohibited, except as authorized by permit or rule. Injection wells incidental to aquifer remediation and
2United States Environmental Protection Agency. 1991. Seminar Publication: Site Characterization for Subsurface Remediation. EPA/625/4-91/026. Center of Environmental Research Information. Office of Research and Development. Cincinnati, OH.
3 United States Environmental Protection Agency. 1993. Suggested Operating Procedures for Aquifer Pumping Tests. EPA/540/S-93/503. Technology Innovation Office, Washington DC.
experimental technologies are distinguished from hazardous waste injection wells and are designated as Class V wells under the UIC program. Class V wells covered by the federal UIC program are authorized by rule and do not require a separate UIC permit. A Class V well regulated by a state may require a permit. Application of UIC requirements depends on the regulatory framework controlling the cleanup with fewer restrictions expected for cleanup activities conducted under CERCLA authority (United States Environmental Protection Agency {U.S. EPA}, 19954). UIC requirements are regularly implemented for RCRA corrective action cleanup projects, but may not be as consistently applied to CERCLA sites.
It is essential that the injection permit documentation list both principal compounds and any unreacted compounds or impurities. One example of this point is the use of sodium chloride (NaCl) as an electrolyte. Most sources of NaCl (including food grade material) will list arsenic as a potential impurity. Hence, the potential arsenic concentration in the injectate (or injected solution) must be considered.
Conducting SEAR requires the recovery of injected solutions containing high concentrations of dissolved or mobilized contaminant and surfactant chemicals. On-site treatment of the extracted groundwater will typically be needed to reduce contaminant concentrations to levels consistent with the permit requirements of the publicly-owned treatment works (POTW), other discharge requirements such as the National Pollutant Discharge Elimination System (NPDES) permit, or for chemical recovery and reuse requirements. Management of other waste streams resulting from wastewater treatment (e.g., DNAPL separated by decanting or air discharged from a stripper) must comply with all applicable federal, state, and local requirements.
Should it prove economical to recycle compounds such as the surfactant and alcohol, regulatory permission for reinjection must be gained. The recycling process involves concentration of surfactant chemicals for reuse and an undesirable effect is the simultaneous concentration of other compounds that may impact surfactant performance (Battelle/DE&S, 2001a5). The feasibility of surfactant reuse is strongly dependent on site-specific regulations, as contaminant removal to maximum contaminant levels (MCLs) prior to surfactant reinjection is cost-prohibitive. Recently completed surfactant floods at former Naval Air Station Alameda Point, CA, and Marine Corps Base (MCB) Camp Lejeune, NC, where permission was granted to reinject surfactant without requiring contaminant removal to MCLs (because hydraulic control of injected fluids had been demonstrated), indicates that controlled reinjection of surfactants may gain widespread regulatory acceptance. As regulatory interpretations allowing the use of injectants have recently become more flexible (U.S.EPA, 20026, 20007), it is possible that a similar trend will follow for the reinjection of SEAR process chemicals.
4 United States Environmental Protection Agency. 1995. Surfactant Injection for Ground Water Remediation: State Regulators’ Perspectives and Experiences. EPA/542/R-95/011. Technology Innovation Office, Washington, DC.
5 Battelle and Duke Engineering & Services. 2001a. Final Technical Report for Surfactant-Enhanced DNAPL Removal at Site 88 Marine Corps Base Camp Lejeune, North Carolina. Prepared on behalf of the Naval Facilities Engineering Service Center for the Environmental Security Technology Certification Program, Arlington, VA.
6 United States Environmental Protection Agency. 2002. Handbook of Groundwater Protection and Cleanup Policies for RCRA Corrective Action. EPA/530/R-01/015. Office of Solid Waste and Emergency Response, Washington D.C.
Vertical gradients in the subsurface system and recoverability of DNAPL fluids may be of concern to regulators at some sites. This may dictate a more conservative design approach, to mitigate potential loss of hydraulic control vertically, as well as to prevent the ultra-reductions of interfacial tension that may result in a mobile DNAPL front (i.e., DNAPL mobilization). Similarly very dense surfactant-DNAPL solutions (e.g., solubilizing 25% or more of DNAPL by weight) may not be permitted, with lesser leeway being given to more dense contaminants, discontinuous and other such complicated lithologies, leaky or fluctuating groundwater conditions and weak capillary barriers. 2.4 Risk Management Issues
Education of technical and project managers is a key factor in reducing misapplication of technology, probable errors in implementation, and for resolving contracting performance issues. For a DNAPL site, the more simple, or homogeneous, the hydrogeology, the more permeable the media to be flooded, and the more competent the underlying capillary barrier, the lower the risk of technology failure. At more complex sites with significant heterogeneities, low permeabilities (< 10-3 cm/sec), or vertical gradient systems, greater expertise is required for comparable performance to the simpler low risk sites. At the time of this publication, it is not recommended to use surfactant flooding on DNAPL sites with fractured media or those without a continuous and relatively impermeable capillary barrier. This includes locations where earlier site investigation activities may have compromised the integrity of the capillary barrier beyond feasible repair. Such sites may result in insufficient hydraulic capture of contaminated fluids regardless of imposed gradients.
Generally, proper recovery and targeting of flooding chemicals necessitates hydraulic continuity of the zones to be flooded under pumping gradients, well-defined vertical and horizontal extent of contamination with the associated permeabilities of these zones, natural and external gradients and any fluctuations of such quantified, and integrity measurements of the underlying and supporting low permeability media that has arrested DNAPL movement downwards. As explained in the SEAR Design
Manual, attentive logging and capillary barrier testing procedures, using the appropriate equipment for
retrieval of completely intact core samples, can provide valuable information on the integrity of the less permeable layers or aquitard maintaining DNAPL above it. Due to flowing sands conditions often encountered during retrieval of soil samples, direct measurement methods (e.g., CPT sensor equipment) may support refined vertical profiling of soil lithology and DNAPL saturations, if both can be obtained real-time simultaneously, to avoid pushing through a formation that is preventing DNAPL movement downwards. Water level data from multiple locations, collected at discrete depth intervals per location, may also indicate confining zone integrity, and geophysical methods used in determining hydrogeologic zone boundaries.2 These procedures, alongside other field design characterization activities, may be best delegated to the vendor contracted to perform the flood for reasons of liability and design aspects. As mentioned above, the breaching of a capillary barrier supporting DNAPL is a concern to be avoided in all cases. More conservative flooding approaches, resulting in less dense DNAPL solutions to be transported through the aquifer, may be indicated by capillary barrier testing results and other DNAPL site characteristics, as mentioned above. Similarly, pumping rate pulsing or pulsing of injectants, which has been investigated, may be unfavorable due to vertical gradients created with significant variability (e.g., turnoff and turn on) of injection pumping rates. Finally, free-phase DNAPL should be removed to the extent feasible prior to introduction of surfactants to reduce unintended mobilization concerns. It may be noted that the above-mentioned admonitions do not apply equally to LNAPL sites with LNAPL contaminants only, as these contaminants will not be mobilized downwards due to gravity.
Additional risk management measures not involving issues for design are discussed in the following on sections.
2.5 Performance Assessment
Performance assessment as a concept has typically been applied to small-scale technology demonstration projects, to provide a benchmark with which to compare, on an even basis, competing innovative technology alternatives. For larger-scale projects, there is usually a trade-off between devoting additional budget dollars towards ‘post-mortem’ site characterization analysis, and operating the remedial system for an extended period with any possible in-the-field system optimization. For contractual purposes, the former may be recommended, to be protective of the environment at a site that poses significant risk if DNAPL becomes mobilized in unwanted directions. This contracting approach would preferably stipulate that the vendor is liable for the uncontrolled DNAPL migration and additionally nonattainment of specific performance objectives (as explained in the paragraph below), akin to an extended service warranty on a consumer product8. As surfactant flooding has seldom been used to address remediation of entire DNAPL source zones impacting a particular contaminant plume, the longevity of a surfactant flooding remediation on the overall plume size has yet to be directly observed, and has thus been the forum of groundwater modeling, which is yet another motivation for the emphasis that has been placed upon accurate and correctly applied baseline and post-remediation performance assessment measures. When a site has already been thoroughly characterized for remediation design as recommended for high performance, the additional investment for post-DNAPL characterization may not be as significant. In all cases, sampling media (i.e., soil to soil or groundwater to groundwater) and sampling intervals (e.g., 6 in. to 6 in. core samples or 2 in. screen to 2 in. screen groundwater samples, all at similar depths) should be comparable for pre- and post- events. An exception is to prevent the hydraulic breaching of a confining layer within a DNAPL zone, most critically prior to remediation; thus, it may be difficult to characterize safely DNAPL distribution in confining zones.
In recent projects, the performance of a SEAR flood has been evaluated primarily by obtaining initial and final DNAPL mass estimates to determine whether percent DNAPL removal objectives have been achieved, as well as by comparing the mass of chemicals injected to the mass recovered to evaluate attainment of chemical recovery (or hydraulic fluid control) objectives. Such has required relatively detailed monitoring operations in tandem with detailed pre- and post-remediation site characterization. The performance (or design) targets for technology demonstrations are often established at over 90% for both contaminant and chemical recovery design parameters. While the former criteria may be relaxed somewhat, the latter pertaining to recovery of injected surfactant chemicals should not be due to the significant increase in contaminant mobility in the presence of surfactant chemicals. Numerous soil samples (sampling volume, locations and depth intervals for accurate parameter estimates as determinable or validatable by geostatistical kriging methods), partitioning interwell tracer test (PITT) data, or a combination of these and other approaches may be necessary to obtain quantitative and validated pre- and post- DNAPL soil estimates. (Recommended DNAPL soil sampling procedures and a discussion of PITTs can be found in the SEAR Design Manual.) Vertical profiling to determine the lithologic layer in which the contaminant continues to be lodged is necessary to determine the remaining risk of DNAPL unremoved following treatment. For example, contaminant remaining lodged in a low permeability clay-containing layer tends to provide a persistent long-term but relatively low-level (i.e., slower mass transfer) contamination source, while contaminant left behind in more permeable and transmissive layers will serve as a greater (i.e., faster mass transfer) but less persistent contamination source.
Whether or not it is possible to determine the error associated with a given DNAPL mass removal estimate, the cumulative DNAPL recovered from each extraction well, in a separate or free-phase, and solubilized forms, can be calculated to estimate the total mass of DNAPL recovered from the subsurface with flooding operations. The accuracy of the mass extraction curve will increase with the number of samples collected and the clarity of resolution within the aquifer will rely as well upon the number of extraction wells selected for detailed sampling. The recovery of DNAPL from selected aquifer strata can also be determined from vertical contaminant recovery distribution profiles obtained from multi—level sampling (MLS) data. As briefly mentioned in the SEAR Design Manual and as further described in Appendix B, multi-level sampling devices permit the collection of numerous depth discrete samples in contrast to those from regular monitoring wells that provide averaged samples from groundwater drawn in over the length of the exposed well screen. If contaminant recovery as observed at the extraction wells is poor, then the surfactant levels in the discrete sampling zones may also provide information about the efficiency of chemical flooding (i.e., effectiveness of chemical penetration into all zones to be remediated). A running estimate of the percentage of chemicals removed from the aquifer with post-surfactant water flooding operations may also be obtained and correspondingly the mass of injected chemicals remaining in the aquifer following flooding operations can usually be obtained of mass recovery curves composed of a sufficient number of samples to appear continuous.
Given that the entire DNAPL source has been treated, which includes the assumption that the source zone has been delineated well enough for remediation of the entire source zone, post-treatment conventional groundwater monitoring in the downgradient or other compliance boundary direction, may supplement other performance data directly from the treatment zone. This may entail encircling the perimeter of the original source zone with wells for a site with variable hydraulic gradients. In the meantime, new technology continues to evolve towards more cost-effective DNAPL detection, and measurement technologies in the subsurface and improved tools for determining the mobility of contaminant away from the source at a selected boundary zone (or contaminant mass flux measurements) continue to be investigated. Currently under evaluation are a variety of pumping, passive diffusion, and other innovative borehole methods to determine whether source reduction measures have impacted dissipation of contaminant from the source zone.
From an operational viewpoint, meeting SEAR performance criteria is dependent on the following:
q Proper wellfield installation, inclusive of well construction and development methods,
q maintaining the quality of injected surfactant chemicals, q maintaining design flowrates in the SEAR wellfield,
q maintaining a sufficient extent of surfactant flooding and post-surfactant injection water flooding operations, and
q monitoring system parameters and recording monitoring data to validate that SEAR performance criteria have been met.
These topics are the subject of Section 4.0. To be protective, monitoring activities to maintain and document system integrity and performance should receive thorough treatment in project planning documents subject to approval by regulatory agencies. These include the workplan as well as sampling & analysis plan.
In summary, it may be noted that performance assessment measures are inclusive of detailed performance monitoring activities to ensure that the surfactant flooding remediation system will operate properly and as designed. Sampling monitoring and system operational data, juxtaposed with initial
design detail, inclusive of modeling simulation predictions, may be used to determine whether the remediation has been successful in achieving design objectives, and in reducing risk to the environment and receptors, subject to confirmation by post-treatment performance assessment characterization, as deemed desirable, feasible, or worthwhile. As emphasized in the SEAR Design Manual and as reiterated here, much will hinge on the initial design characterization, as proper system monitoring itself may not be possible without sufficient information and interpretive expertise from earlier completed stages of the project.
2.6. Site Coordination Requirements
There will be a number of issues to discuss with the facility in order to properly specify site mobilization and system construction requirements, including the availability of local equipment and on-site operators. This will require coordination on items ranging from utilities needs to delivery of bulk items, to community public relations and hazardous waste removal from the site.
2.6.1 Water and Utilities
SEAR operations will require a potable water source, electricity, compressed air and in some instances, natural gas or propane for the operation of heated wastewater equipment. If compressed air (for pneumatic equipment) is not available, on-site generation of compressed air by an electric-powered compressor is an alternative. Therefore the basic utility requirements are a reliable source of potable water and electricity to sustain injection and extraction operations for the duration of the project. Water in sufficient quantities is generally available, but for large-scale projects (e.g. > 50 gallons per minute system) may require notifying the utility supplier to install larger diameter lines and to ensure a continuous supply of water for the project duration. With respect to electricity, the proper phase, amperage, and voltage must be available. If sufficient power is available from the public supply company, it can still often mean that a line or lines must be dropped into the site and transformers installed. One advantage of connecting to a public supply network is that it can be a more reliable source, than portable generators. When comparing the relative costs of a public supply versus on-site generation of electricity, the reliability of the source may add value to the public supply network. In either case, a contingency power source may be necessary if power outages are expected.
If electric power is to be supplied by generators, it will be necessary to locate a provider. It is generally prudent to have extra generation capacity on-site in case of mechanical device failure. The generators will be supplying power on a continuous basis, 24 hours per day, for the duration of the project and the vendor from which the generators are to be rented should be informed that the generators will be operated more than 8 hours per day. This fact will alter the maintenance and replacement schedule the vendor has for the generators. The method used to refuel portable generators is an additional consideration. Hauling fuel to the site daily in 5-gallon cans is the least desirable option. Contracting with a local fuel supply company to bring a fuel truck to the on either a set schedule or on an on-call basis is often the most attractive option. Refueling considerations will also be applicable to fuel-powered compressors if used. Finally, the power generated by portable generators is often not “clean” enough to operate sensitive equipment such as gas chromatographs without line filters added; however this may also apply to existing utility lines which require transformer devices.
2.6.2 Miscellaneous Logistics Coordination
It will be necessary to coordinate with local wastewater treatment facilities or waste contractors to determine the available capacity and costs of discharging to their facility relative to onsite wastewater treatment processing. Additionally, particularly with oily combustible mixtures, there may be a resale
value associated with reuse of recovered NAPL liquids; therefore, such opportunities should be investigated in advance. Used chemical drums may be recycled.
Project scheduling will require arrangements with local staff members to avoid interfering with operating facilities and existing activities. During surfactant flooding remediation, vicinity pumping should be reduced to avoid any additional gradients to the areas being treated by surfactants. Arrival of rental equipment, equipment trailers, piping/hosing, bulk chemicals (e.g., drummed, palleted, and tankered) as well as miscellaneous delivered hardware components, will require facility coordination to arrange paved road accessibility rights and receiving locations for air-shipped items. Anticipated chemical storage and trailer areas should be coordinated with local authorities ahead of arrival so that designated areas may be appropriately delineated and labeled with placarding and project notification signs. Local authorities and residents should be notified of the anticipated project duration and 24 hour per day nature of flooding operations.
2.7. Pilot-Scale Investigations
Pilot-scale studies may be desirable to investigate system performance and cost feasibility prior to a full-scale effort or when a risky situation is encountered, such that difficulty exists for maintaining hydraulic control over surfactant laden DNAPL contaminated fluids (e.g., tidal fluxes or other vertical gradients in the vicinity of the treatment zone), or when a weak capillary barrier system exists. The chemical compatibility of surfactant for the contaminant(s) and aquifer formation may also be confirmed during a pilot-scale study; however, bench-scale surfactant selection testing with site groundwater and soils can be performed in place of more expensive field testing if this is the only requirement. Recoverability of surfactant laden with DNAPL fluids can be somewhat gauged by a conservative tracer test under a given set of design pumping rates (i.e., injection and extraction rates) through examination of tracer recoveries. However, only a surfactant injection (with extraction) test will provide information about recoverability of surfactant-laden solutions under pumping conditions. Finally, flooding variants such as the use of polymer and/or surfactant foam for even fluid propagation across a heterogeneously composed aquifer stratigraphy will be the greatest benefit of pilot testing to refine design injection and extraction parameters. When sufficient injection pressures and/or hydraulic gradients can be maintained, most sites will exhibit improved flooding efficiency with the addition of mobility control refinement to circumvent preferential flow in the vicinity of low permeability silty layers commonly sinks for DNAPL.
Surfactant foam flooding mobility control design will require specifying a design pulsing rate of air to create foam within the desirable (and clean) layers. While laboratory-based foam formation studies (AATDF, 1997)9 will be needed to evaluate the influence of contaminant and surfactant formulation properties on foaming mobility and stability, only a field foam propagation study9,10 will reveal whether horizontal traverse of foam under specified air pressures is sufficient to divert surfactant fluids through lower permeability zones for the air pressures applied. Thus, a pilot investigation may be helpful in examining the feasibility of foam propagation when mobility control is to be used. On the
9 AATDF. 1997. AATDF Surfactant/Foam Process for Aquifer Remediation. Prepared for The Advanced Applied Technology Demonstration Facility, Houston, TX by Intera Inc.
10 Hirasaki, G.J., Jackson, R.E., Jin, M., Lawson, J.W., Londergan, J., Meinardus, H., Miller, C.A., Pope, G.A., Szafranski, R., and Tanzil, D., 2000. "Field Demonstration of the Surfactant/Foam Process for Remediation of a Heterogeneous Aquifer Contaminated with DNAPL," NAPL Removal: Surfactants, Foams, and
Microemulsions. Fiorenza, S., Miller, C.A., Oubre, C.L., and Ward, C.H. Editors. Lewis Publishers, Boca Raton, (2000), 1-166.
other hand, polymer addition for mobility control, particularly for removal of contaminants of greater viscosity than water, increases the viscosity of the flooding solution and will require higher induced gradients for capture of contaminated and remedial fluids. Pilot testing can determine whether the gradients necessary for capturing DNAPL and polymer-surfactant fluids can be maintained for improved contaminant contact and recovery compared to an unamended (without polymer mobility control) system. Similarly, if heating is deemed necessary to assist in mobilizing a viscous contaminant, pilot testing can assist in feasibility evaluations.
When intended only for a portion of the entire source zone area, a pilot-scale investigation should occur ideally in the upgradient portions of the source zone area. This will ensure minimum disturbance of streamlines within the test zone caused by any existing containment pumping that can not be turned down, and protect the zone being flooded from subsequent recontamination by DNAPL outside of the treated zone to maximize the benefit of the pilot study remediation effort. As earlier mentioned, as much free-phase NAPL should be removed from zones adjacent to the targeted remediation zones as possible to facilitate meaningful collection of any post-treatment monitoring data, as well as for the longevity of remedial efforts. When inaccessibility issues arise, such as DNAPL located beneath a building in use, remediation efforts should consider hydraulic isolation of these zones. The above issues apply equally to a full-scale remediation that is performed in a modular fashion to reduce equipment capital costs.
Section 3.0: SEAR SYSTEM COMPONENTS
This section seeks to clarify the major equipment items in use with and components of in-situ surfactant flooding operations. Following the process design and initial planning stages, design operating parameters such as the durations of flooding phases (i.e., aquifer preparation flooding, surfactant flooding and post-surfactant water flooding), required chemical quantities, and individual well pumping rates, will be specified for a given estimate of DNAPL mass and distribution. Implementation of surfactant flooding remediation will require further engineering design and construction of the flooding system components to allow continuous delivery of enhancing or remedial fluids and recovery and handling of spent surfactant solution and contaminants. The sizing of field equipment may occur once the available capacity of on-site or vicinity wastewater treatment facilities has been evaluated and confirmed. It may thus be more feasible to address the source zone in sections proceeding from upgradient to downgradient portions as recommended, to reduce any treatment plant construction costs as well as the cost of any additional fluids processing to recycle surfactant chemicals. Administrative or management constraints may also influence the scale of flooding system construction activities. The major surfactant-enhanced flooding system components are introduced below.
3.1 Component Description
A SEAR project requires equipment and components to conduct the following major field tasks:
q Preparation of surfactant solution and other injected chemical solutions; q Injection and extraction operations;
q Monitoring of system parameters;
q Maintenance of critical system design parameters; q Wastewater treatment.
The operational criteria for these tasks and their associated equipment, hardware and materials of construction where relevant (e.g., for chemical compatibility) are discussed in the sections that follow. 3.1.1 Chemicals Preparation.
There are in general three options for preparing chemical solutions for delivery on a SEAR project:
q Batch (tank) mixing; q In-line mixing; and
q Pre-mixing or off-site preparation.
These options may be applied to the preparation of two types or compositions of solutions that are injected during SEAR flooding operations: surfactant solutions and water flood or hydraulic control solutions. Surfactant solutions are commonly comprised of a surfactant, salts of sodium and/or calcium, and a cosolvent. Occasionally, a polymer may be added as well. Water flooding and hydraulic control solutions consist of potable water mixed with the same electrolyte at the same or lower concentrations as used for the surfactant mixture, and will be referred to in further discussion as electrolyte solution.
3.1.1.1 Batch Preparation Method. Batch preparation methods are the most common method of preparing chemical solutions in the field for small-scale surfactant flooding projects. Mixing conditions within tanks can be created with recirculation pumps that draw fluid from the bottom of the tank for discharge at the top of the tank. The tanks will require fittings for drawing fluids in this manner. To decrease the amount of time required to mix the injected batch, a mixing pump should be
obtained that provides for a flowrate capacity sufficient to ensure adequate time to prepare additional batches such that only well-mixed fluids, passing quality standards (to be discussed in Section 4), are delivered for injection. The viscosity and composition of the unmixed injectate must also be considered in selecting recirculation pumps for mixing. A pump and tank configuration is shown in Figure 3-1.
Fiberglass or composite plastic tanks can be used for blending and storage of the surfactant, alcohol, and electrolyte solutions. The specification of the tank materials should be based on an evaluation of the chemicals that will be stored in the tanks to ensure that the tank materials are compatible. An array of high density polypropylene (HDPE) tanks used for blending electrolyte solutions is shown in Figure 3-1. Composite plastic materials are generally chemically compatible and resistant to most of the chemicals used on SEAR projects and are easier to handle when empty because of their relatively low weight. For mixing and storage of the injectates or solutions to be injected, multiple tanks will be necessary to allow for the injection of a mixed batch and the concurrent mixing of additional batches. A minimum of two tanks is recommended for surfactant preparation with one tank for mixing and the other tank for storage of the mixed solution. This ensures that sufficient injectate quantities are continuously available for injection. In general, the minimum capacity of the storage tanks should be at least 150% of the expected volume of chemical solution delivery. For injectate preparation on SEAR projects, tank volumes of 6,000 gallons or less, consisting of composite plastic materials are commonly used.
Figure 3-1. HDPE Storage Tanks Used for Blending Electrolyte Solutions
Surfactant and cosolvent chemicals are usually delivered to the site in drums or in bulk tank cars and will need to be transferred to tanks for batch mixing. The viscosity of most surfactants used in SEAR projects is in the range of 40 to 1000 centipoise (cP), (depending on the purity of the surfactant preparation from the manufacturer that can be variable), which is significantly more resistant to flow
than water that possesses a viscosity of 1 cp. When transferring viscous surfactants and surfactant solutions through hoses and tubing, additional head losses will be encountered, which should be accounted for in specifying the pumping capacity and line diameters. When transferring alcohol on-site, extreme caution must be taken to ensure that the pump type and construction materials do not create a flammable or explosive situation during the transfer process.
3.1.1.2 In-Line Mixing Method. To mix chemical solutions in-line, hydrodynamic mixers installed in the injection line are used in lieu of batch mixing tanks and recirculation pumps. This method of mixing is an innovation derived from the food industry and requires less tankage than the batch mixing method for supplying high flow volumes of surfactant solutions and to accommodate relatively small footprints. In-line mixing requires that injectate components be accurately metered into a potable water stream so that the mixture contains the appropriate chemical concentrations. The chemicals are staged in relatively small tanks in pure form or high concentrations and then metered into the injectate stream for mixing at the hydrodynamic mixer. Properly selected chemical transfer pumps and flowmeters or metering pumps can be used for chemical metering. This method greatly reduces injectate mixing time, but relies heavily on the accurate metering and performance of the equipment items, which will be operated 24 hours per day during flooding operations.
3.1.1.3 Pre-mixing or Offsite Chemical Preparation. When it can be arranged with a chemical manufacturer, pre-mixing of supplied chemicals may prove to be the most cost-effective option for preparing surfactant solutions. This will provide the most consistent quality of surfactant solution for flooding operations. Surfactant, cosolvent (if used) and electrolyte are pre-mixed at the vendor facility for delivery to the site. Electrolyte solutions for hydraulic control wells will still require batch mixing preparation. For premade solutions delivered to the site, the storage volume should be based upon the turnover or use of the chemicals with a storage capacity for a one-week or a one-month supply being desirable depending on the environmental stability of the chemical compound solutions to be stored.
3.1.2 Injection and Extraction Operations.
A simplified process flow diagram of injection and extraction operations with control instrumentation is provided in Figure 3-2. Water injection or hydraulic control wells supplement extraction wells for maximum containment and recovery of injected fluids. Automated process control and data acquisition for continuously monitored pumping operations is addressed further in Section 3.1.4.
Injection and extraction operations require properly constructed injection and extraction wells alongside standard equipment items that include injection and extraction pumps and controllers, flowmeters and a combination of hoses, tubing, pipes and valves for carrying fluids to and away from the treatment zone. In-line filters will be needed upstream of pumps and flowmeters to protect against damage and poor performance from particulate materials, such as any undissolved impurities from chemical solution tanks and soil fines removed from extraction wells. Reformulation of recovered surfactant fluids for reinjection may result in precipitation of iron and cationic species from solution and require additional filtration prior to reintroduction to the aquifer. Backup power generation equipment is suggested for continuous pumping operations, and pumping power hookup should consider minimizing the time to switch to a backup power source when a power-out alarm is sounded.
3.1.2.1 Injection and Extraction Wells. Proper well construction is perhaps one of the most important, yet often poorly accomplished, aspects of addressing NAPL remediation. It is a major component in the success of a SEAR project, as maximizing the available pumping gradients is
Figure 3-2. Basic Surfact
ant Flooding
critical to recovering contaminated fluids of elevated density and viscosity relative to water. For this reason, well construction methods used for SEAR wells, are more detailed and demanding than for conventional groundwater monitoring wells. Existing wells pre-dating discovery of DNAPL zones may best be used to supplement surfactant flooding operations as groundwater sampling and water level monitoring locations, as relevant.
Following SEAR design, the well locations and screen intervals and depths will be known and well construction can begin. To ensure that well construction is consistent with the stratigraphy and contamination at the site, the following should occur:
q Screen placement across the contaminated stratigraphy of interest. Furthermore, at DNAPL sites, the bottom of the well screens in recovery wells should be installed across the lower capillary barrier/aquifer interface (this allows for uninhibited DNAPL migration into the well). At LNAPL sites, the screens should span the oil/water interface and be long enough to meet the demands of the SEAR design. Well construction should not allow cross contamination between aquifers.
q Well screen and filter pack sizes should be properly selected based upon the particle size of the aquifer material.
q Well materials should be chosen based on their chemical compatibility with the contaminant(s) and other SEAR chemicals as well as their physical compatibility with pressure or heat stresses that may be exerted.
q Injection and recovery well screens should be continuous wire wrap (this improves well efficiency and allows for superior well development).
q Wells must be accurately placed within the desired depth interval and not offset by conditions such as flowing sand.
q Wells should be installed using centralizers to ensure placement in the middle of the borehole.
q Drilling fluids should be selected that do not inhibit well development, thereby decreasing well efficiency.
q The volumes used and placement of the sand/gravel filter pack should be carefully monitored to insure that the filter pack fully surrounds the well screen.
Detailed recovery well construction specifications intended for duplicate use in DNAPL site characterization and surfactant flooding remediation were provided in the design manual and have been included as Appendix A within this document. Occasionally, wells installed during the DNAPL investigation phase are screened over the improper depth intervals, or demonstrate poor efficiency. If the well is screened to the appropriate final depth, it may still be used for mobile DNAPL removal, and perhaps for injection activities with the use of an inflatable packer to modify the screen interval as applicable. Wells that perform poorly during tracer injection or extraction activities should be redeveloped and replaced if feasible.
3.1.2.2 Pumps and Plumbing. With the completion of design simulations, the required flowrates and head differential for establishing hydraulic control will be known. This information is used to select pumping equipment. The optimum pump configuration to maximize well fluid recovery uses dedicated extraction pumps for each well. When selecting downhole submersible pumps, such as those used frequently for recovery operations, consideration must be given to the diameter of the well, the number of pumping zones per well, the lift and flowrate required under maximum viscosity conditions, and the chemical compatibility of the pump materials with the effluent. In practice, even if the mobilization of NAPL is not anticipated during surfactant flooding, it is recommended to design for this possibility. As 24 hour per day operation will be required, equipment reliability will also be a
major criterion of all pumps selected. Finally, spare pumps should be readily available for contingency use.
The plumbing conduits of a SEAR system for injection and extraction operations include pipes, tubing and hoses. Selection of appropriate materials, such as steel or polyvinyl chloride, should be based on factors including cost, pressure rating, and chemical compatibility with surfactant fluids and NAPL11 (in the recovery lines). Manifolding of injection or extraction lines requires piping material construction. Otherwise where possible, flexible tubing or hoses are more convenient for mobility and construction.
Valves are used to control the movement of fluids through pipes, tubing, and hoses, such as for sampling fluids and flowrate measurement and control. Valve types used on a SEAR project include ball, gate and needle valves. Ball and gate valves are commonly used for on/off control of fluids, and can also be used for rough flowrate control. Needle valves are used for more precision in flowrate control. Valves that are electronically actuated will be required for automated flowrate and pressure regulation. As with other plumbing material types, cost, pressure rating, and chemical compatibility with fluids should be considered when selecting valve material types.
3.1.3 Monitoring System Parameters.
Monitoring equipment is used to collect data to gauge SEAR progress and to maintain and refine SEAR system operating parameters. Throughout a SEAR project, fluid chemistry, fluid flow properties and aquifer properties are regularly monitored. Table 3-1 shows the most important system monitoring parameters and common monitoring locations. For performance monitoring of a surfactant flooding operation, groundwater samples are most easily collected from extraction wells. However, groundwater samples collected at these locations will not provide vertical performance data. A multi-level sampler (MLS) network within the extraction wells can provide undiluted groundwater samples at depth discrete intervals, more accurately reflecting the capacity of the surfactant formulation and contact of discrete aquifer zones through a heterogeneous aquifer. Appendix B discusses MLS devices in further detail.
Specific conductance, temperature and pH can be measured with manually operated meters or using in-line probes, particularly for process monitoring of effluent fluids. Flowrates and system pressure can be measured using calibrated in-line flowmeters and pressure instruments. Electronic pressure transducers or transmitters and manual water level meters can be used to determine the elevation of the water surface within and adjacent to the treatment zone.2,12 Interface probes can determine the in situ depth and corresponding volume of DNAPL within a well. DNAPL volume may also be determined using a graduated glass cylinder or similar device after pumping or bailing from a well. Sampling of monitoring points can occur either intermittently, whenever a sample is scheduled for collection, or continuously (i.e., with continuous pumping) at low flowrates. Intermittent sampling of wells or multilevel samplers is typically conducted using surface pumps, while continuous sampling
11 United States Environmental Protection Agency. 1995. Nonaqueous Phase Liquids Compatibility with Materials Used in Well Construction, Sampling and Remediation. EPA/540/S-95/503. Technology Innovation Office. Washington DC.
12 United States Environmental Protection Agency. 1985. Practical Guide for Ground Water Sampling. EPA# CR-809966-1. Illinois State Water Survey Contract Report #374. Prepared in cooperation with Robert S. Kerr Environmental Research Laboratory, the Environmental Monitoring Systems Laboratory, Las Vegas,
Table 3-1. SEAR System Monitoring Parameters
Category Monitoring Parameter Monitoring Location
Fluid chemistry Temperature, pH Specific conductance Electrolyte
Cosolvent Surfactant
Contaminant (NAPL volume and dissolved concentration of each component)
Mixed injectate (tank or injection line), extraction wells and monitoring points(a)
Extraction wells and monitoring points(a)
Fluid flow properties Pumping flowrates Pressure
All pumping locations Injection, extraction and wastewater processing fluid lines
Aquifer Properties Water levels
Free-phase NAPL levels
Injection and extraction wells and monitoring wells
Check for in all wells being monitored during flooding operations
(a) Refers to monitoring wells, multi-level samplers (MLS), and monitoring points for wastewater treatment processes
often utilizes submersible pumps. Low flowrate pumps such as peristaltic and bladder pumps are commonly used for sampling purposes. Sampling pumps, filter devices, tubing points and materials, as well as sampling well points, should be chemically compatible with NAPL in the aquifer.
Extraction well line sample retrieval can be accomplished using in-line sampling equipment that can be electronically actuated. With appropriate well sampling accessories, in-line sampling devices can be used in tandem with autosampler equipment and gas chromatography (GC) components adapted for surfactant solutions and high organic compound loading to quantify cosolvent and solubilized contaminant concentrations. This type of system can provide near real-time concentration data for monitoring of multiple effluent lines. Monitoring of surfactant concentrations, such as for maintaining injectate quality and performance capabilities of wastewater treatment processes, will require titration or HPLC equipment. Alternatively, a surrogate organic compound, such as the cosolvent co-eluting with the surfactant, which requires only appropriately fitted GC equipment for measurement, may be used to estimate surfactant concentrations. Analytical methods are discussed in Section 4.2.3. Surfactant titration equipment is detailed further in Appendix C.
3.1.4 Process Control System.
Due to the extent of data collection activities for system monitoring on SEAR projects, automated data recording devices are suggested. Electronic monitoring equipment for injection and extraction operations can be incorporated into a data acquisition system (DAS) for automated data logging and feedback process control. A centralized user interface may be attached for data access and viewing. Such is known as a Supervisory Control and Data Acquisition system (SCADA). A SCADA system for SEAR incorporates electronic monitoring and control devices for automated measurement and regulation of flowrates, system pressure, water levels and other parameters as desired. An assembly of SEAR components that includes SCADA control features is displayed in Figure 3-2. Aboveground treatment operations will typically require separate control systems and displays for different monitoring features.
System software is used for interactive control of SCADA components and must be customized for each project to address the site-specific number of items such as injection wells, extraction wells, sampling parameters and sampling frequencies. Automatic shut-off devices and alarming features may also be incorporated with the inclusion of a SCADA system. Most SCADA components are integrated within a system control trailer that is plumbed to injection and extraction lines. Although a SCADA system will still require periodic calibration using manual measurements and more hardware to assemble, there can be a significant reduction in the labor requirements that attend 24-hour field operations. Continuous system monitoring will generate a much higher volume of data for SEAR documentation and performance evaluation, and this data can be efficiently collected and viewed in electronic format.
3.1.5 Wastewater Treatment.
The principal unit operations for a SEAR wastewater treatment system and selection criteria, including commercial availability of separation systems developed and tested for surfactant/cosolvent flooding wastewaters, are described in thedesign manual. Technologies for contaminant removal may include conventional processes such as air-stripping and steam-stripping, or innovative processes such as liquid-liquid extraction and pervaporation, depending on surfactant chemical recovery requirements and contaminant effluent properties. Once the bulk of strippable or contaminated compounds are removed, biological treatment may be used with a sufficient residence time for surfactant degradation. However, more typically, surfactant may be allowably discharged (under permit) into another off-site wastestream, and as such it will often contain foam suppressing chemicals; on the other hand, it may also be concentrated for reuse on-site by filtration and foaming methods both necessitating the absence of foam suppressants.
In addition to aqueous-phase organic compound removal equipment, pretreatment and auxiliary equipment will frequently include:
q Decanting equipment (or separators) to remove free-phase NAPL;
q Chemical metering equipment to adjust pH and dispense antifoaming agent; q Surge/Process storage tanks; and
q Contingency storage tanks.
A UV sterilization or chemical amendment unit to destroy microorganisms in the process water may be necessary if biofouling is anticipated to adversely affect the treatment process. Similarly, additional filtration devices may be required to capture suspended particulates (i.e., fines and precipitates) that may cause fouling of thermal treatment lines and membrane modules when used.
Bag filters (i.e., 1 to 25 mm filters)13 are effective in removing such particulate matter without pressure drop concerns. Appropriately rated pumps will be required to move fluids from one process unit to another. Plumbing networks of piping, tubing and hoses with valves and gauges of compatible and process-rated materials will provide controlled fluid movement throughout the system.
Additional tankage to accommodate possible system modifications (such as increased pumping rates) as well as effluent streams which fail discharge permit limits should be readily available. For surge/process storage tankage, chemically compatible thermoplastic storage tanks can be used once DNAPL is mainly removed. Metallic or stainless steel tanks and drums are commonly used for storing DNAPL fluids. For contingency tankage, oil-field frac tanks or tractor-trailer tanker trucks are generally used given their larger capacities, rental availability, and trailer mobility. Secondary containment will be necessary for tanks and plumbing containing chemical solutions, as further discussed in the next section. As shown in Figure 3-3, wastewater treatment equipment may be contained within a tented facility with plumbing to wastewater discharge tankers, including bypass hosing to the tankers for emergency operations. Containment lining can be constructed during tent installation using wood berming about the perimeter of the tent frame to elevate the flooring edges of an appropriate liner material.
Figure 3-3. Temporary Tented Wastewater Treatment Facility
13 Vane, L.M., Hitchens, L., Alvarez, F.R., and E.L. Giroux. 2001. “Field demonstration of pervaporation for the separation of volatile organic compounds from a surfactant-based soil remediation fluid.” Journal of Hazardous Materials, B81 (2001), 141-166.
3.2 Systems Components Preparation
During system mobilization and assembly, some components will require calibration, leak and failure checking, and conditioning against inclement weather and potential system failures.
Appropriate calibration and testing equipment will be needed to maintain operability of pumping equipment and data logging devices both within specified ranges. Components that fail calibration testing should be repaired or substituted prior to initiating flooding operations; this applies particularly to commonly rented equipment such as water quality measurement probes and pumps. If used for on-site operations, GC equipment, i.e., detectors, and any transducing equipment, such as actuated sensors and other automated devices, will also require calibration. Health and safety instruments, such as a combustible gas indicator, should be periodically calibrated prior to use.
Flowmeters and metering devices can be calibrated by taking an average of several manual flowrate or fluid delivery measurements (e.g. bucket tests). Of particular importance is that the flowmeter be rated for the viscosity of the fluid it is intended to monitor and that the fluid being monitored itself is used during the calibration process. Water quality probes and pressure transducers should be calibrated in accordance with the manufacturer’s guidance. Pumps should be individually checked for leaks and malfunctions. Potable water should be used to test system components for proper flow routing and leaky connections. Flow-related devices should be tested at the highest and lowest anticipated flowrates to verify that all valves, flowmeters, pressure gauges, and plumbing will operate as designed and not malfunction.
Some equipment may require protection from inclement weather to avoid unexpected system failures and operational complications. Pumps and other outdoor electric equipment should be weatherized (with appropriate covers) and be properly grounded with ground fault interruptors (GFI). Sensitive electronic equipment should be safeguarded against exposure to heat, light and moisture and be equipped with properly conditioned power sources where relevant (e.g. GC equipment). Any SCADA and DAS components should be equipped to minimize the impact of potential power interruptions.
Tank storage areas will require secondary containment that can hold a volume equal to 110% of the largest tank contained, unless otherwise stipulated by local regulatory authorities. High density polyethylene (HDPE) landfill liner can be used to construct most secondary containment. Experience has shown that the HDPE liner should be at least 20 mils thick and of the ‘cross-linked’ variety. For effluent tanks, it should be noted that HDPE is not compatible with chlorinated solvents, but there are few acceptable materials that can be otherwise used. Sheets of plywood can be laid over or under the liner to reduce puncturing. The walls of the secondary containment system are often constructed with straw bales or with fencing materials. A secondary containment liner is shown in Figure 3-1. Site drainage should be directed away from wells and drum storage areas as much as possible using appropriately constructed drainage diversion and/or collection systems.